RESEARCHING MAINTENANCE

Eric Liskey

Pine tree trimming
I am seeing a lot of pine trees with side branches being stub-cut. I assume this is to reduce the weight of the branch. Won't the branches eventually die? - California

That depends on what's left of the branch after it's been cut. Dr. John Ball, a forester with South Dakota State University, explains that without any lateral branches, the remaining stub will eventually die. This will occur as the existing living needles finish their normal life span, typically 2 or 3 years, but perhaps longer, depending on the species of pine. However, if lateral branches remain on the cut limb, growth can continue and the branch should survive.

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The key is the presence of an apical bud on lateral branches, says Ball. Pines only form them on the candles. That's why recommendations for pinching back pines typically call for doing so during candling. Pinching out the apical bud at this time will prompt new lateral buds and shoots to form. Heading back branches at any other time will simply result in a stub that eventually will die back - either to the next lateral or completely to the trunk.

Chemicals to control buttonweed
I am having trouble controlling Virginia buttonweed. What are the chemical options for treating this weed? - Texas

This weed has become one of the more notorious pests of Southern turf. Few herbicides are labeled specifically for its control, and even then, the degree of control may not be ideal.

One option is imazaquin (BASF's Image). This product is labeled for buttonweed, but only provides suppression.

Dr. Bert McCarty of Clemson University recommends three-way phenoxy herbicides, particularly those containing 2,4-D, which is the most-effective phenoxy product on this weed. McCarty recommends a follow-up application in 3 to 4 weeks for better control.

A third option lies in a relatively new product: Riverdale's Manor herbicide. This uses the active ingredient metsulfuron, and its labeled weeds include Virginia buttonweed.

Made in the shade
What is the most shade-tolerant warm-season turfgrass? I maintain some fully shaded areas, and the bermudagrass just won't make it. - California

I asked Dr. Philip Busey, with the University of Florida, about this. He suggested that some dwarf St. Augustinegrass varieties may provide the most viable options. Several show good shade tolerance relative to other warm-season grasses. Zoysiagrass will probably perform better than bermudagrass, but not as well as the St. Augustinegrass varieties.

California does not utilize St. Augustinegrass to the extent that the Gulf Coast states do, so availability might be a problem. Check with local sod suppliers to see what they offer. You also should consider non-turf options for the most deeply shaded areas. Such locations can be difficult for even the most shade-tolerant turfgrasses. Shade-tolerant perennials are good way to avoid the continual battle of maintaining turf in deep shade.

One obvious benefit of installing large-caliper trees is the more mature appearance they provide to a landscape. However, there is a limit to the size of root ball you can dig and move. As a result, larger specimens often are transplanted with proportionately smaller root balls.

Previous research has indicated that the initial size advantage of larger trees may be lost over a several-year period because the smaller trees are able to become established more quickly, presumably because of their more-intact root system. This leads to higher growth rates than for larger trees, which take longer to establish after transplanting. A new study has reached a different conclusion, however.

In 1996, a group of Ohio researchers transplanted small (1.4-inch caliper) and large (3.3-inch caliper) red oaks that had been lined out as whips in 1993 and 1988, respectively. Among other factors, the researchers noted pre-transplant vigor of the trees. They then documented the growth and establishment of the transplanted trees for 4 years.

Contrary to the findings of some other studies, the larger trees displayed post-transplant growth that equaled or surpassed that of the smaller trees. There was a catch, however. This involved only those trees that survived. While none of the smaller trees died after transplanting, 58 percent of the larger trees died. (The researchers account for this, in part, by the fact that the trees were not root-pruned in the nursery. Thus, digging removed a large amount of the larger trees' major roots.)

The researchers point out an interesting fact. Large trees transplanted to landscapes often are simply those that are chosen last from growing blocks. That process is not random, of course. The last remaining trees frequently are the least vigorous specimens, which explains why they were passed over. Comparing their establishment rates to those of smaller transplants may not be a valid test and could explain why these results seem to contradict the findings of previous studies, some of which did not control for factors such as plant vigor.

Regardless, the researchers make one recommendation that few would dispute: When choosing a large tree, select from a block grown specifically for large size. Avoid the "leftovers" of a block that has been picked over.

After the Environmental Protection Agency's recent actions regarding chlorpyrifos (Dursban) insecticide, many in the industry worried about the fate of other important insecticides. Only a few broad-spectrum insecticides are available with the wide range of uses of chlorpyrifos. After its demise, other insecticides became that much more important.

Diazinon is one such product. Fortunately, it appears that the EPA is likely to allow continued use of diazinon for most, if not all, of its current landscape uses. For example, according to a press release issued by Novartis (which manufactures the active ingredient), the EPA considers granular diazinon to have an acceptable margin of safety under the new Food Quality Protection Act rules. It creates no dietary or ground-water risks.

Unfortunately for the greenhouse industry, Novartis has chosen not to support greenhouse or other indoor uses of diazinon. Additional data demanded by the EPA to support such uses was considered prohibitively expensive to produce, so Novartis decided instead to discontinue those uses.

This was a predicted consequence of the FQPA, enacted in 1996. Many foresaw that the additional studies necessary to meet the new, more-stringent FQPA registration requirements would cost so much money to perform, that it would make more sense, economically, to simply withdraw the product (or at least certain labeled uses), regardless of the actual risk posed by the pesticide. The current situation, though fortunate for grounds care professionals, is a manifestation of this.

Several months ago, we ran a piece concerning cocoa-hull mulch indicating, among other things, that its availability in bulk form could be limited, because this is an imported product. And in most locations, this is true: Cocoa hulls are expensive and may only be available in bags. However, a knowledgeable reader has informed us that chocolate-processing plants in the United States often dispose of cocoa hulls by selling them in bulk for use as mulch. So if you're in the market for cocoa hulls, and you know of a nearby chocolate factory, check there.